This project has been studying the characteristics and uses of creatine kinase isoenzymes as markers of cancer and of myocardial insult. During the current period, the BB isoenzyme of creatine kinase (CK-BB) was measured in serum, tumor homogenates, cell culture homogenates and CSF using a radioimmunoassay developed in this laboratory. CK-BB is consistently present in elevated concentrations in small cell cancer of the lung (SCCL), but not in other lung tumors. It is also associated with carcinoma of the prostate. This study (a) continues investigating the biochemistry of SCCL and its variants, (b) finishes a project exploring the use of CK-BB to monitor response to therapy of prostatic cancer, (c) extends this work to examine CK-BB in breast cancer, and (d) measures CK-BB in CSF of patients with brain metastases.